Ejemplo Modo Directo

Ahora veremos un ejemplo del funcionamiento del modo directo, el código siguiente es simple pero suficiente para mostrar los resultados del proceso.

Se tiene el código de la función de prueba sub1, el cual incluye las variables que designamos como activas first and other.

      subroutine sub1(first, other, third, out, res)
      real first, other, third, out, res
      include 'globals.inc'
c start mixing all variables :
      out = first*other + 3.0*third
      res = sin(first) + cos(other)
      first = 2.0 * first
      third = 2.0/other
c now overwrite some values...
      if (first.gt.other) then
         first = cos(out)
         other = 1.0
      else
c ...in one or in all cases
         first = exp(out)
         other = 1.0
      endif
      end

código resultado de la diferenciación automática.

      SUBROUTINE SUB1_D(first, firstd, other, otherd, third, thirdd, out
     +                  , outd, res, resd)
      REAL first, firstd, other, otherd, out, outd, res, resd, third, 
     +     thirdd
      REAL x(14), y
      COMMON /cc/ x, y
      INTRINSIC COS, EXP, SIN
C start mixing all variables :
      outd = firstd * other + first * otherd
      out = first * other + 3.0 * third
      resd = firstd * COS(first) - otherd * SIN(other)
      res = SIN(first) + COS(other)
      first = 2.0 * first
      thirdd = -(2.0*otherd/other**2)
      third = 2.0 / other
C now overwrite some values...
      IF (first .GT. other) THEN
        firstd = -(outd*SIN(out))
        first = COS(out)
        other = 1.0
        otherd = 0.0
      ELSE
C ...in one or in all cases
        firstd = outd * EXP(out)
        first = EXP(out)
        other = 1.0
        otherd = 0.0
      END IF
      END